Hitherto, it has been known that a number of compounds which induce vascular smooth muscle to relax by inhibiting influx of calcium ions into cells are useful in the treatment of diseases in cardiac circulatory. As such compounds, for example, calcium channel inhibitors and sodium channel inhibitors have been already developed, and, further, many studies on potassium channel activators have been made. Examples of such potassium channel activators include Pinacidil used frequently as a capillary vasodilator drug; Nicorandil used as an anti-stenocardia drug; and Cromakalim used as an anti-hypertension agent.
European Patent Publication No. 093,535 filed by Beecham Group, plc. in the title of "novel chromene and chroman" discloses benzopyran derivatives of formula (A) and salts thereof: ##STR5## wherein: one of R.sup.a and R.sup.b is a hydrogen atom and the other is selected from the group consisting of a C.sub.1-6 alkyl- and alkoxycarbonyl, C.sub.1-6 alkyl-carbonyloxy, C.sub.1-6 alkylhydroxymethyl, nitro, cyano, chloro, trifluoromethyl, C.sub.1-6 alkyl- and alkoxysulfinyl, C.sub.1-6 alkyl- and alkoxysulfonyl, C.sub.1-6 alkyl- and alkoxycarbonylamino, C.sub.1-6 alkyl- and alkoxysulfinylamino, C.sub.1-6 alkyl- and alkoxysulfonylamino, C.sub.1-6 alkyl- and alkoxythicarbonyl, C.sub.1-6 alkyl- and alkoxythiocarbonyloxy, C.sub.1-6 alkylthiomethyl, formyl, an optionally substituted aminosulfinyl, aminosulfonyl or aminocarbonyl, or a terminal substituted ethylenyl, --C(C.sub.1-6 alkyl) NOH, and --C(C.sub.1-6 alkyl)NNH.sub.2 group, or
one of R.sup.a and R.sup.b is nitro, cyano or a C.sub.1-6 alkylcarbonyl group and the other is methoxy or an optionally substituted amino group; PA1 one of R.sup.c and R.sup.d is a hydrogen atom or a C.sub.1-4 alkyl group, and the other is a C.sub.1-4 alkyl group, or PA1 R.sup.c and R.sup.d together form a C.sub.2-5 polymethylene; PA1 X' is an oxygen or sulfur atom; PA1 Y' and Z' are a hydrogen atom, respectively, or together form a single bond; and n is 1 or 2. PA1 R.sup.f is a hydrogen atom, or a lower alkyl or phenyl group; PA1 R.sup.g is a hydrogen atom or a lower alkyl group; PA1 R.sup.h is a hydrogen atom or a hydroxy group; and, PA1 R.sup.i is a hydrogen atom; or R.sup.h and R.sup.i together form a single bond; and PA1 R.sup.j is an aryl- or N-heteroaryl group whose 2-position is a hydroxy group, or an N-oxide group in the case of N-heteroaryl group. PA1 R.sub.3 is a C.sub.1-4 straight or branched alkyl group; and PA1 R.sub.4 is ##STR10## wherein R.sup.G and R.sup.H are, each independently, a C.sub.1-6 alkyl group or an optionally substituted phenyl group; A and B are, each independently, S or O; and Z is a C.sub.1-3 straight or branched alkyl group.
Further, European Patent Publication No. 298,452 A2 filed by F. Hoffmann La Roche & Co. discloses benzopyran derivatives of formula (B) and pharmaceutical compositions containing same: ##STR6## wherein: R.sup.e is a hydrogen or halogen atom, or a trifluoromethyl, nitro, cyano, a lower alkyl, lower alkoxycarbonyl, lower alkylthio, lower alkylsulfonyl, lower alkanoyl, carbamoyl or mono- or di(lower alkyl) carbamoyl group;
The above compounds have been reported to be useful in the treatment of hypertension. However, another use of the compounds was reported in references such as Br. J. Pharmacol. 89, 395-405(1986), Br. J. Pharmacol. 165, 231-239(1989), and Br. J. Pharmacol. 95, 765-770(1988): i.e., the compounds may be used as a bronchodilator in addition to a blood pressure-lowering agent, since they can relax smooth muscle by enhancing the hyperpolarization of the plasma membrane of a cell. Accordingly, the above compounds have the disadvantage of a lower selectivity with respect to the anti-hypertension activity.